Method of nerve stimulation and a stimulator for the application of the method

Abstract

In order to excite living cells, a FM transmitter transmits for a period t at a frequency f such that the difference between f and a reference frequency f O sets the amplitude of a desired nerve stimulation pulse. A receiver implanted in the living body is inductively coupled to the transmitter and processes the signal so as to obtain an output signal having an amplitude which is proportional to the frequency deviation. The duration of the stimulation pulse is adjustable independently of the amplitude. The output signal is applied between two electrodes which are implanted in the vicinity of the cells to be excited and can be multiplexed to excite several pairs of electrodes in succession by an electronic circuit advanced by signal segments at a frequency at one end of the deviation range.

We claim: 
     
       1. A method for electric excitation of living cells by means of an electromagnetically inductive receiver implanted in a living body and equipped with output electrodes, comprising the steps of: producing an alternating electromagnetic induction field at the location of said receiver of a frequency variable about a reference frequency f 0  by means of a transmitter external to said body operated at a frequency f so set and for a period so selected that the requency difference f -f 0  corresponds to a desired amplitude of a cell excitation pulse and the selected period corresponds to a desired cell excitation pulse duration, and repeating said field producing step at predetermined intervals to the extent further cell excitation is desired;   detecting said induction field in said receiver to collect energy therefrom for operating said receiver, and   detecting in said receiver the extent of said frequency difference f -f0 of said induction field and producing in response thereto at said output electrodes a cell excitation signal of an amplitude corresponding to said frequency difference f -f 0  and of a duration determined by said selected period.   
     
     
       2. A method as defined in claim 1 in which between some successive performances of said field producing step the following additional steps are performed: producing for a period of time an alternating electromagnetic induction field at a frequency outside of the frequency range utilized for producing a cell excitation signal,   detecting such period of said production of a field of a frequency outside said cell excitation frequency range, and   switching the output of said receiver, in response to the performance of the last-mentioned detecting step, to a different pair of cell excitation electrodes among a set of a plurality of pairs of cell excitation electrodes implanted in said living body, said switching step being performed progressively among said pairs of electrodes in response to successive performances of said detecting step respectively in successive performances of the method.   
     
     
       3. A method for electric excitation of living cells by means of an electromagnetically inductive receiver implanted in a living body and equipped with output electrodes, comprising the steps of: producing an alternating electromagnetic induction field at the location of said receiver by means of a variable frequency transmitter external to said body successively at frequencies f 1 ,f 2  f i  2 f i  respectively for durations t 1  t 2  . . . t i  ;   detecting said induction field in said receiver to collect energy therefrom for operating said receiver, and   detecting in said receiver the several frequencies f 1 , f 2  . . . f i  and in response to at least one of them switching the output of said receiver from one to another pair of cell excitation electrodes among a set of a plurality of pair of cell excitation electrodes implanted in said living body, and in response to others of said frequencies f 1 , f 2  . . . f i  producing at one pair of said electrodes a cell excitation signal of an amplitude and polarity determined by the difference between the particular frequency and a reference frequency f 0  and of a duration determined by the corresponding of the period durations t 1 , t 2  . . . t i .   
     
     
       4. A stimulator for implantation in a living body and there delivering, by means of electrodes, pulses which are capable of electrically exciting living cells in response to a frequency modulated electromagnetic transmitter external to said living body, said stimulator comprising, in combination: a receiving coil tuned to a predetermined reference frequency f 0  ;   first detecting means responsive to the output of the receiving coil for delivering a continuous d.c. signal having a duration equal to the duration of an alternating current signal obtained at the output of the receiving coil;   stabilizing circuit means responsive to said first detecting means for providing a continuous d.c. output signal having a constant as well as a duration equal to the duration of said alternating current signal;   frequency detection means, having a first input connected for response to the output of said receiving coil and having a second input connected to the output of said stabilizing circuit, for delivering an output signal having a magnitude which is proportional to the difference between the detected frequency f and said reference frequency f 0  during a time interval t equal to the duration of said alternating current signal obtained at the output of the receiving coil and for delivering no significant output at other times;   pulse shaping circuit means for producing a cell stimulating pulse in response to the output of said frequency detection means, having a control input connected to the output of said frequency detection means, said pulse having an amplitude which is proportional to said frequency difference f -f 0  and a duration determined by said time interval t, and   output means, including electrodes implanted in said living body, responsive to the output of said pulse shaping circuit means for providing cell stimulating pulses to living cells adjacent to said electrodes.   
     
     
       5. A stimulator as defined in claim 4, in which said output means comprises a power stage for driving said electrodes in response to the output of said pulse shaping means. 
     
     
       6. A stimulator as defined in claim 4, which further comprises: switch control pulse producing means responsive to the output of said frequency detection means;   a second receiving coil tuned to a frequency outside the range of frequencies utilized for producing cell stimulation pulses;   second detecting means responsive to the output of said second receiving coil for detecting said second frequency outside a range of frequencies utilized for producing cell stimulation pulses;   a control counter connected to the output of said switch control pulse producing means so as to be advanced thereby in response to said output and connected to the output of said second detecting means so as to be reset thereby, and   switching means responsive to said control counter for sequentially switching, to connection with the output of said pulse shaping means, different electrode pairs of said electrodes for sequential stimulation of different cells in response to successive portions of the output of said pulse shaping means.   
     
     
       7. A stimulator as defined in claim 4, including means for deriving power from the output of said first detecting means and thereby supplying all the electric power needed for the operation of the receiver, said power deriving means including a connection between said output of said first detecting means and said pulse shaping circuit for energization of the latter. 
     
     
       8. A stimulator as defined in claim 6, in which said switch control producing means is constituted to provide an output for advancing said counter in response to an output of said frequency detection means corresponding to a frequency which is closer in value to said reference frequency than frequencies utilized for producing cell stimulation pulses.